Method for recycling plastic materials and use thereof

Abstract

The invention relates to a method for recycling plastic materials which contain at least two polymers, copolymers or blends thereof based on polystyrene. The plastic material is thereby mixed with a solvent for the polymers, copolymers or blends. Subsequently a precipitation is effected by addition of a corresponding precipitant so that then the gelatinous precipitation product can be separated from the further components of the plastic material. The method is used for recycling of any plastic materials, in particular of plastic materials from electronic scrap processing and from shredder light fractions.

The invention claimed is: 
     
       1. Method for recycling plastic materials which contain at least two polymers, copolymers or blends thereof, each of which is based on polystyrene in which
 a) the plastic material is mixed with at least one solvent for the polymers, copolymers or blends thereof 
 b) at least one precipitant which is miscible with the at least one solvent is added to the solution of the polymers, copolymers or blends thereof for precipitation of the at least one polymer, copolymer or blend thereof in gelatinous form, the at least one precipitant and/or the quantity thereof being chosen such that the mixture of solvent and precipitant has a value for the hydrogen bonding strength δ H  of the Hansen solubility parameter of 10 to 15 √{square root over (MPa)} and 
 c) at least two gelatinous precipitation products, each with different adhesion properties, are separated from each other by thoroughly mixing so that the adhesion forces outweigh the dispersion energy supplied by the thorough mixing so that the at least two gelatinous precipitation products are demixed completely from each other and the further components of the plastic material. 
 
     
     
       2. A method according to  claim 1 , wherein the mixture of solvent and precipitant has a value for the hydrogen bonding strength δ H  of the Hansen solubility parameter of 11 to 13 √{square root over (MPa)}. 
     
     
       3. A method according to  claim 1 , wherein the solvent in a) is selected from the group comprising ketones, ether, cycloalkanes, esters, in particular acetone, methylethylketone, tetrahydrofuran, dialkylester of dicarboxylic acids and fatty acid alkylester. 
     
     
       4. A method according to  claim 1 , wherein the precipitant in b) is selected from the group comprising water, alcohols, in particular methanol, ethanol, isopropanol, n-propanol and butanol or mixtures thereof. 
     
     
       5. A method according to  claim 1 , wherein after step a), components of the composite material which are non soluble are separated mechanically. 
     
     
       6. A method according to  claim 1 , wherein the mechanical separation is effected by filtration. 
     
     
       7. A method according to  claim 1 , wherein the precipitation is effected at temperatures up to 170° C. 
     
     
       8. A method according to  claim 1 , wherein the precipitation is effected at temperatures up to 100° C. 
     
     
       9. A method according to  claim 1 , wherein at least one precipitation product is dried before separation in step c). 
     
     
       10. A method according to  claim 1 , wherein at least one precipitation product is dried after separation in step c). 
     
     
       11. A method according to  claim 9 , wherein the drying is effected by means of rotational evaporation. 
     
     
       12. A method according to  claim 1 , wherein subsequently the at least one separated polymer gel is pressed through perforated matrices to form strands. 
     
     
       13. A method according to  claim 1 , wherein the copolymers and blends of polystyrene are styrene-butadiene (SB), styrene-acrylonitrile (SAN), acrylonitrile-butadiene-styrene (ABS), acrylic ester-styrene-acrylonitrile (ASA) or blends thereof. 
     
     
       14. A method according to  claim 1 , wherein the plastic material further comprises a polymer components. 
     
     
       15. A method according to  claim 14 , wherein the further polymer components is a polyolefin, polyamide, polyvinylchloride, polyurethane, polycarbonate, polyacrylate, polymethacrylate, polyester resin, epoxy resin, polyoxyalkylene, polyalkylene terephthalate, polyvinyl butyral or a copolymer or blend thereof. 
     
     
       16. A method according to  claim 14 , wherein the further polymer components are separated preceding step a) by means of a density separation. 
     
     
       17. A method according to  claim 16 , wherein further non-polymer components of the plastic material are separated in the density separation. 
     
     
       18. A method according to  claim 1 , wherein the plastic material further contains a low molecular additive. 
     
     
       19. A method according to  claim 18 , wherein the low molecular additive is a flame-retardant additive, a softener and stabiliser. 
     
     
       20. A method according to  claim 19 , wherein the flame retardants is a brominated flame retardant. 
     
     
       21. A method according to  claim 19 , wherein the is a phthalic acid ester, adipinic acid ester, aliphatic C 4 -C 8  carboxylic acid or a polyalkylene glycol. 
     
     
       22. A method according to  claim 18 , wherein the low molecular additives remain in step b) in the solution and thus are separated from the precipitated polymers. 
     
     
       23. A method according to  claim 20 , wherein said brominated flame retardants is polybrominated diphenylether, polybrominated biphenyl, bis[dibromopropoxydibromophenyl]propane, hexabromodecane or bis-(tribromophenoxy)ethane.